Introduction

There are numerous and varied modes of reproduction within Anura. One such mode that has evolved independently at least three times is that of constructing and depositing eggs into a foam nest (Duellman and Trueb, 1986). A multitude of breeding studies report on the behavioral aspect of foam nest construction.

© 2002 Jean-Marc Hero Leptodactylus knudseni producing a foam nest. “The nest is constructed of glandular secretions beaten into a froth, the consistency of which is quite like a beaten egg white” (Heyer, 1969).

However, relatively few studies have considered the site of production of the liquid that is beaten into foam and whether any morphological or histological modifications are present in the reproductive tract of those species that create foam nests.

In all foam-nesting species described in the literature, and all those examined in this study, the posterior region of the oviduct showed a definite enlargement. This enlarged region of the oviduct is actually comprised of a series of oviducal folds that are compacted together into what has formerly been called a ‘foam gland’ (Coe, 1974; Kabisch et al., 1998).


Materials and Methods

Data on the reproductive tract, with emphasis on the oviducts, was obtained for 20 female specimens - representing 13 different foam-nesting species. Width measurements of the oviducts were made at standard points to allow for cross species comparisons. Photographs were taken of the oviducts and they were described qualitatively. Oviducal tissue samples from 9 different species were prepared for light microscopy.

Oviducts of Leptodactylus podicipinus

Oviducts of Leptodactylus fuscus

Research Questions

• Do all females that are foam nesters have an enlarged region of the oviduct or ‘foam gland’?
  
  
• Do males of foam-nesting species contribute any type of secretion to the foam nest or show any morphological modifications of the reproductive tract?
  
  
• Does the size of the foam nest correspond to the size of the females enlarged oviducal region?
  
  
• How does the histology and cell type of the enlarged oviducal region compare to the non-enlarged regions of the oviduct and to that of closely related species that do not construct foam nests?
  
  
• What is the nature of the secretion – is it excess egg jelly or some type of unique substance?
  
  
  

Results and Conclusions

• All foam-nesting species examined showed, to varying degrees, an enlarged and compacted region of the posterior oviduct.
  
  
• The one species examined that was not a foam nester did not have this enlarged and compacted structure.
  
  
• The males that were examined showed no reproductive system modification strongly suggesting that the female secretion alone is what is used to construct a foam nest.
  
  
• The size and structure of the ‘foam gland’ showed much variation among different species. This interspecific variation likely corresponds to the specific size and location of the foam nest.
  
  
• The histology of the ‘foam gland’ revealed many folds of densely packed cells of a secretory nature.
  

Acknowledgments

I would like to thank Helen Wimer for expertly preparing slides of oviduct material. I thank Jon Norenburg for allowing me use of his camera and microscope and Addison Wynn for help interpreting the histological sections. Philippa Horton gave valuable advice and sent her Ph.D. thesis. I would like to thank my funding source, the NMNH Office of the Director.